Corrosion-resistant and cold workable molybdenum steel



Pateii ted Niar. 15, 1238 CORROSION-RESISTANT AND COLD WORK- -ABLEMOLYBDENUM STEEL Heinrich Reitz, Bitterfeld, and Erich Hengler andAlfred Biittinghaus, Wetzlar, Germany No Drawing. Application May 'I,1936, Serial No. 78,316. In Germany May 7, 1935 5 Claims.

The present invention relates to steels capable of resisting attack bycorrosive media including aqueous solutions of chlorine, hypochlorousacid and their salts.

One of the chief problems with which the present day metallurgists arefaced is a meeting of the demand by the chemical arts for steels whichwill withstand corrosive chemicals and still be capable of beingmechanically worked. This problem is particularly onerous as regardsthose industrieswhich employ solutions of chlorinecontaining substances,since, as is known, ferrous metals are very susceptible to attack bythese substances. In fact, screens and the like used in filteringapparatus in the manufacture of hypochlorites, when made of so-calledstainless steel, are so vigorously attacked that their utility iscompletely impaired after only short periodsof service.

Chromium is one 'of the alloying elements which is most commonlyemployed in steels designed for use in chemical apparatus. This elementhas the function, among others, of improving the corrosion resistance ofthe steel. Molybdenum has recently come into rather extended use,usually with chromium as an ,agentfor in-, creasing or impartingcorrosionresistance. Neither this element nor chromium, nor bothtogether, however, is capable of giving steels this property to anextent sufiicient to withstand the attack of different chemicalsespecially solutions of chlorine-containing substances. Moreover,molybdenum, when used in large amounts, has a marked tendency to renderste'els brittle thereby impairing their capability of being mechanicallyworked in the cold, that is cold rolled,.cold drawn and cold hammered.Any increase in corrosion resistance resulting from the use of largepro- I portions of molybdenum is, therefore, offset by a decrease in themechanical cold workability of the steels.

The purpose of this invention is to provide a chromium-molybdenumlow-carbon steel which will be resistant to attack by aqueous solutionsof chlorine, :hypochlorous acid, their salts and the like, and at thesame time willpossess the desired mechanical properties of being coldrolled, cold drawn, cold hammered and the like to a high degree.

'- We have discovered that if there is included in low'carbon-chromium-molybdenum steels an alloying ingredient capable offorming carbides, in such quantities that after a fixing of the freecarbon as carbide there remains sufi'lcient of the ingredients to formmixed crystals with the other alloying ingredients, steels of aresistance to chlorine-containing solutions which could not be'foreseenare obtained. The alloying ingredient that we have found most siutablefor use and which we therefore prefer, is titanium. However, otherelements may be used in lieu of titanium with satisfactory results.Thus, such carbide-forming elements as vanadium, tantalum, uranium,niobium, cerium, boron, zirconium and tungsten may be used assubstitutes for titanium.

As previously noted, we have found it preferable in making up our alloysto maintain a low content of carbon, that is less than about .5%. Thechromium content of the alloys should range between about 12 and 30%,preferably between about and The molybdenum content may be as high as 5%and should exceed about 1.5%. The titanium or other carbideforming-element should be present in an amount. of from about .5 to3.5%.

and less than .5% of silicon. The balance of the 1 steel is iron withthe usual negligible quantities of impurities generally present instainless steels.

These steels especially when prepared with titanium, not only areremarkably resistant to corrosion by chlorine-containing solutions butalso possess the property of being cold rolled, cold hammered and colddrawn. An estimate of their resistance to corrosion may be gleaned fromthe fact that said steels are capable of withstanding attack by the verycorrosive calcium hypochlorite solutions even at a temperature of 110 C.Said steels may, therefore, be employed for all purposes where steelsofthese properties are required. Thus they are admirably fitted for themanufacture of wire screens for filtering chlorineandhypochloride-containingmashes and lyes and perforated supporting discsfor such filters as well as armatures, armature accessories, pumps,containers, valves, slide bars and the like which during use contactchlorine-containing solutions.

The following illustrates typical alloys'within the scope of ourinvention:'

- I g Per cent 1. Carbon :less than 0,50

Manganese 0,30- 0,60 Silicon =less than 0,50 Chromium 12,5 -30,0Molybdenum 1,50- 5,00 Titanium 0,50- 3,50 Balance iron and negligiblequantities of usual impurities.

Per cent 2. Carbon :less than 0,10

Manganese 0,40- 0,60 Silicon =less than 0,50 Chromium 16,0 -18,0Molybdenum -i 1,80- 2,40 Titanium 0,80- 1,20 Balance iron and negligiblequantities of usual impurities.

Per cent bium, cerium, boron, zirconium or tungsten. '3. Carbon F '0,20-0,30 However, when such metals are used in lieu of Manganese 0,40- 0,60titanium, it is preferable to maintain the propor- Silicon =less than.0,50 tions of elements of Example 5. Chromium 23,0 -25,0 Titanium hasheretofore. been used in steels Molybdenum 2,80- 3,30 but primarily forthe purpose of effecting de- Titanium' 1,80- 2,40 oxidation thereof.This use is in no way com- Balance iron and negligible quantities ofusual impurities.

Per cent 4. Carbon 0,18- 0,22 Manganese 0,40- 0,60 Silicon =less than0,50 Chromium 27,0 29,0 Molybdenum. 1,60- 2,00 Titanium 1,20- 1,60

Balance iron and negligible quantities or usual impurities.

. Per cent 5 Carbon =less than 0,50

Manganese 0,40- 0,60 Silicon =less than 0,50 Chromium 20,0 -30,0.Molybdenum 1,80- 4,00 Titanium 0,50- 3,50

Balance iron and negligible quantities of usual impurities. 4

parable toour use of titanium. On the contrary, the presence of titaniumin our steels serves the purposes of augmenting the corrosion resistanceof the steel imparted by the molybdenum and 01! preventing themolybdenum from destroying the desired mechanical properties of thesteel such as its cold rollability, cold ductility and coldmalleability. Thus, the steels have a much greater resistance tocorrosion than could be imparted to them by molybdenum alone, and at thesame time are capable of being mechanically worked in the cold despitethe presence of substantial quantities or molybdenum.

The two fold function of the titanium in our steels is developed in theaccompanying tables which compare the corrosion resistance and coldmalleability oi chromium-molybdenum steels withchromium-molybdenum-titanium steels.

Low 0! weight in grams/sq. meter of surface in 1 hour Depth inmm. inaAcetic c M 51 Cr Mo 11 :32 107 H1864 5 5 3:8. 0 -H% m 5 5 tcm- BNO; Mmto temtem- Erichramm sen g C. turo Loss 0! weight in grams/sq. meter ofsurface in 1 hour I llgepth NaOCi ,3?- SOlllUOlJ oil! 207 gg mm.in 8 0Mn Si Cr Mo T 107 6 gm5 ag:

8 4 +4% chlorine 80mm 83 HNOI Del It I Erlclb ZPC. at. and400 n 20Cgrams oi 0801: at 20C 0,27 o,40-0,co o,ao-l 24,83 2,0 "10,5 0,021 a m n6,5

X] 0,07 0, 40-0,60 0,30-1 26,70 2,30 10,0 sliligng 7,1

, mg. 0,!) 0,40-0,60 0,30-1 26,28 1,88 1,39 0,00 0,0058 lfgckat- 7,50,08 0,40-0,60 0,30-1 29,15 1,71 1,29 0,00 0,0000 lie at- 8,2

' ac 0,27 0,40-0,60 0,30-1 26,28 4,00 4,5 Fitting. N01;

' workable.

The titanium in any of these alloys .may be Thefasteris'ks in the abovetables indicate that 7 replaced by vanadium, tantalum, uranium, niotheresults were not ascertained with particularity since it was apparentfrom observation that the test pieces had'suflered a very materialdecrease in weight, a fact which was to be expected at the outset.

For a full discussion of the Erichsen test referred to in the tablesattention is directed to page 154 of Enzyklopaedie tier technischenChemie by Ullmann, volume 4, 2nd edltio What we claim is: 1. Coldductile and cold malleable corrosionresisting alloys for use in themanufacture of articles which require resistance to attack by aqueoussolutions ,of chlorine, calcium hypochlorite and their salts, containingless than .5% of carbon, from about .3 to about .6% of manganese, lessthan about .5% of silicon, from about 12 to about 30% of chromium, fromabout 1.5 to about 5% of molybdenum, and from. about .5 to about 3.5% ofa carbide-forming element selected from the class consisting of titaniumand vanadium in an amount of about 6 to 12 times the amount of carbonpresent, the balance being. iron with a the usual impurities,

2. The alloy as defined in claim 1, wherein the carbide-forming elementis titanium.

3. Cold-ductile and cold malleable corrosionresisting alloys consistingof Per cent Carbon =less than 0,10 Manganese 0,40- 0,60 Silicon =lessthan 0,50 Chromium 16,0 -18,0 Molybdenum- 1,80- 2,40 Titanium 0,80- 1,20

impurities.

Balance iron and negligible quantities of usua impurities.

4. Cold ductile and cold malleable corrosionresisting alloys consistingof Per cent Carbon 0,20- 0,30 Manganese 0,40- 0,60 Silicon ==less than0,50 Chromium 23,0 -25,0 Molybdenum 2,80- 3,30 Titanium 1,80- 2,40

Balance iron and negligible quantities of usual impurities.

5. Cold ductile and .cold malleable corrosionresisting alloys consistingof Balance iron and negligible quantities of usual HEINRICH ERICHHENGIER. -ALFRED-BU'ITINGHAUS.

